1. Field of the Invention
This invention relates to a focus detecting apparatus which is mounted In a camera or the like.
2. Description of Related Art
In the past, many of the so-called projection and reception type focus detecting apparatus have been known in which a beam of light emitted from a light source is projected toward an object and reflected light from the object is received to thereby measure a distance to the object. In particular, a technique called a multipoint range measurement is being chiefly used in which distances to plural points on the object are measured over a wide area to derive the information of a range measurement therefrom so that what is called an object omission is prevented.
Although this technique brings about appreciable results, most of the projection and reception type focus detecting apparatus chiefly used at present are such that an IRED (infrared-emitting diode) is used in the light source to measure distances to three to five points on the object. With such an apparatus, when a zoom lens markedly changing a field angle is used, it is difficult to make the range measurement most suitable for preventing the object omission in the range of variable magnification from a wide angle to a telephoto position.
In addition, another technique of radiating light beams from some light sources toward the object at the same time has the defect that the intensity distribution of reflected light from the object by respective beams is liable to overlap as the number of focus detecting points is increased, and precise range measurements cannot be made.
In recent years, to obviate this defect, techniques, such as those set forth In Japanese Patent Preliminary Publication Nos. Sho 58-93040 and Sho 61-68221 and Japanese Patent Publication No. Hei 1-57891, have been proposed. These techniques are such that the surface of the object is scanned with a projected beam of light to allow the range measurement in a wider area. Any of the techniques, however, requires a large-scale device for moving the light source itself or rotating a projection unit or the whole of a projection and reception unit.